1. Technical Field of the Invention
The present invention relates to a method of producing a surface-treated steel sheet.
2. Description of the Related Art
A method using chemical conversion treatment or electrolytic treatment is widely employed as a method of forming an oxide layer of which the main component is an oxide of metal, such as Zr, Al and Ti, on a metal base material. In the method using chemical conversion treatment, a metal oxide layer is formed on a metal base material such that: the metal base material is dipped in a treatment liquid; etching treatment is performed for a surface of the metal bate material; the pH in the vicinity of the surface of the metal base material is increased thereby to deposit a metal oxide on the surface of the metal base material. In the method using electrolytic treatment, a metal oxide layer is formed on a metal base material such that: the metal base material is dipped in a treatment liquid; hydrogen is generated at a surface of the metal base material by means of electrolysis of water; and the pH in the vicinity of the surface of the metal base material is thereby increased to deposit an oxide.
When a surface-treated steel sheet obtained by forming a metal oxide layer on a metal base material is used as a material for metal cans, etc, the material is used after being coated with an organic resin layer, such as coating material and layer, in general. Therefore, the metal oxide layer formed on the metal base material is required to have enhanced interfacial adhesion with the organic resin layer.
To this end, for example, Patent Document 1 (Japanese Patent Application Publication No. 2010-13728) discloses, as a method of enhancing such interfacial adhesion between the metal oxide layer and the organic resin layer, a technique of adding an organic resin component to a treatment liquid that contains metal ions when forming the metal oxide layer by means of chemical conversion treatment or electrolytic treatment using the treatment liquid so that the metal oxide layer to be formed contains the organic resin component.